Hairy lustrous yarn

ABSTRACT

A hairy lustrous yarn of isotactic polypropylene which has a rectangular cross section and a luster index above 2. The method of making same which comprises: A. MELT EXTRUDING A MELT-EXTRUDABLE ISOTACTIC POLYPROPYLENE BLEND IN THE FORM OF A RIBBON. B. IMMEDIATELY GAS QUENCHING THE RIBBON TO A TEMPERATURE ABOVE THE GLASS TRANSITION TEMPERATURE OF ISOTACTIC POLYPROPYLENE. C. ATTENUATING THE QUENCHED RIBBON AT A TEMPERATURE ABOVE SAID GLASS TRANSITION TEMPERATURE. D. GAS FIBRILLATING THE ATTENUATED RIBBON.

United States Patent Rassart Feb. 29, 1972 [54] HAIRY LUSTROUS YARN [72]Inventor: Nestor Sylvain Rassart, Drummondville,

Quebec, Canada [73] Assignee: Chemcell Limited, Montreal, Quebec,

Canada [22] Filed: Nov. 13, 1969 [21] Appl.No.: 871,648

Related US. Application Data [63] Continuation of Ser. No. 709,458, Feb.29, 1968,

3,242,035 3/1966 White ..28/1X 3,361,859 l/l968 Cenzato.. ...264/210UX3,366,722 H1968 Tessier ..264/168 Primary Examine -Stanley N. GilreathAssistant Examiner-Werner H. Schroeder Attorney-Leonard Horn and StevenMurphy [57] ABSTRACT A hairy lustrous yarn of isotactic polypropylenewhich has a rectangular cross section and a luster index above 2.

The method of making same which comprises:

a. melt extruding a melt-eirtrudable isotactic polypropylene blend inthe form of a ribbon.

b. immediately gas quenching the ribbon to a temperature above the glasstransition temperature of isotactic polypropylene.

c. attenuating the quenched ribbon at a temperature above said glasstransition temperature.

d. gas fibrillating the attenuated ribbon.

1 Claims, 5 Drawing Figures Patented Feb. 29, 1972 v GR 2 QM... NA/WA gINVENTOR Nestor Sylvuin RASSART Y [j PATENT AGEN T J HAIRY LUSTROUS YARNThis is a continuation of application Ser. No. 709,458, filed Feb. 29,1968, now abandoned.

This invention relates to a remarkably bright hairy polypropylene yarn,and to the process of making the same, especially to a continuousprocess.

Generally, polypropylene is extruded as filaments. The filaments arethen stretched and heat relaxed in an oven to produce a crimp yarn whichhas elastic properties, but no special brightness.

There has now been found a new bright yarn which may easily be produced.The yarn is generally manufactured by melt extruding polypropylene intoa ribbon, immediately quenching the latter to a temperature still abovethe glass transition temperature of isotactic polypropylene andsuccessively attenuating at a temperature above the glass transitiontemperature of isotactic polypropylene and gas fibrillating said ribbon.

In a particular embodiment, before extrusion, the polypropylene ismelted and, once in the molten stage, a viscosity gradient is allowed todevelop by heating preferentially one side of the molten material. Themolten material is then extruded as a ribbon in a directionsubstantially perpendicular to the direction of the gradient, the ribbonis immediately gas quenched. It may then be stretched and gasfibrillated.

Still in another embodiment, one side of the ribbon producing die may beinsulated so as to produce a viscosity gradient on the ribbon atextrusion. As the ribbon leaves the extruder, it is immediately airquenched to a temperature above the glass transition temperature of theisotactic polypropylene and successively attenuated at a temperatureabove the glass transition temperature of polypropylene, gas fibrillatedand heat relaxed.

The polypropylene, which may be used in accordance with the invention,is melt-extrudable isotactic polypropylene, commonly used for theproduction of polypropylene yarn and the like. The isotacticpolypropylene, in powder form, is generally blended with conventionalstabilizers. Pigments, dye additives and other ingredients may also beadded, if desired. However, these materials should be used in limitedquantities so as not to have an adverse effect on the properties of therib-- bon and the yarn resulting thereof.

Before melt extrusion, the polypropylene and the other materials shouldbe well mixed to ensure the production of a ribbon of uniformcharacteristics. Mixing may be carried out in any conventional way. Meltextrusion is then generally carried'out at a temperature between 230 C.and 260 C.

Any apparatus generally used for the melt extrusion of polypropylene andwhich is provided with a ribbon-producing die may be used. The extrudersas described in French Pat. No. 1,405,360 dated May 27, 1964, orCanadian application Ser. No. 008,l53 filed Dec. I9, 1967 or U.S. Pat.application 691,569 filed Dec. 15, 1967, Franklin James, mayadvantageously be used providing that the spinnerette is replaced by aflat or circular film-producing die. If a flat film producing die isused, the ribbon has ends or selvedges on the sides. With a circularfilm-producing die, a fibrillated hose is obtained. The hose is moreuniform and may be drawn or stretched as a two-layer flat sheet. Drawingof hoses is easier in comparison to single sheets which possess hems.After extrusion, it is important to cool the ribbon immediately but to atemperature still above the glass transition temperature of theisotactic polypropylene. This operation seems to establish a viscositygradient within the ribbon. In a preferred embodiment, air is blasted onthe ribbon as it emerges from the lips of the die. Though air is used,any inert gas, which will not react with the ribbon, may be used.

The ribbon, which has low tensile strength at this stage, is heated anddrawn or stretched, while hot, with-conventional stretching apparatus.The hot-melt drawing or attenuating operation is carried out attemperatures between 60 C.-l 10 C., and preferably l l C. The drawingratio is generally from 2 to and preferably near its maximum.

After drawing, the ribbon is usually gas fibrillated by passing itthrough an air jet. The yarn thus obtained may then be collected by anyknown means. If desired, any other gas which will not affect thechemical properties of 'the ribbon may be used.

As already mentioned, if a viscosity gradient is set in the ribbon priorto extrusion, the ribbon formed may not only be air quenched andsuccessively attenuated and gas fibrillated but also heat relaxed toproduce a hairy lustrous crinkled yarn.

Having now generally described the invention, the following drawingswill serve to illustrate particular embodiments of the invention inwhich:

FIG. 1 is a schematic view of a setup for producing bright yarnaccording to the invention.

FIG. 2 is an enlarged cross section of the lowest portion of the die ofFIG. 1, taken along line 2-2.

FIG. 3 is the top view of the cooling device of FIG. 2.

FIG. 4 is a cross-sectional view of a gas jet.

FIG. 5 is a cross-sectional view of a yarn produced in accordance withthe invention.

The setup of FIG. 1 comprises a melt-extruder which is partly shown at10, having at its end a nut 12 for retaining the die shown in FIG. 2 as50. Adjacent to the die a cooling device 14. As soon as the ribbon 16emerges from the die it is quenched by gas arriving from inlets l8 and19 (shown on FIG. 2) of the gas-quenching device, but the temperature isnot permitted to drop below the glass transition temperature ofisotactic polypropylene. After cooling, the ribbon 16 moves around afirst guide roll 20 and between nip rollers 22. Thus ribbon is pulledout at constant speed, which is regulated according to the size of theyarn desired.

The ribbon 16 passes around a second guide roll 24, into inlet 26 of aheating tube 28, and through the heating tube 28. As it leaves theoutlet 30 of the heating tube 28, the ribbon I6 is passed between asecond pair of nip rolls 32. Both sets of nip rolls 22 and 32 aredriven, the nip rolls 32 being driven at a faster speed than the niprolls 22, so as to cause the ribbon to be attenuated during its passagethrough the heat tube 28. The heat stretching tube 28 may be one asdescribed in principle in Canadian Pat. No. 699,470 or copending U.S.application Ser. No. 488,832 filed July 26, 1965, now U.S. Pat. No.3,277,228. Other conventional stretching devices may be used, ifdesired. After being attenuated, the ribbon passes around guide roll 34and through gas jet 38, where it is fibrillated and becomes a hairy yarnof remarkable brightness. The yarn is made up of filaments havingrectangular cross section. The width of the filaments corresponds to thethickness of the stretched film and their length depends upon theefficiency of the fibrillation process used and is a function of suchvariables as pressure, residence time, geometry of the channel.

The yarn is then pulled around a pair of nip rolls 40 and wound up by 'aconventional takeup device 42 which has a speed controller 44.

The extruder head and the cooling device are better shown on FIG. 2. Theend of the extruder comprises (shown on FIG. 2) a die 50 and a gasket 52which are secured to the extruder head by means of nut 12. The die 50has an elongated slot 54 through which the film or ribbon l6 emerges.The width of the slot is generally 0.04 inch or less. The gasket 52,which prevents cooling of the die, has an orifice which is larger thanslot 54; As soon as the ribbon 16 emerges from the die, it is quenchedabove the glass transition temperature by the cooling device 14 whichhas gas inlets l8 and 19.

In another embodiment of gasket element 52 covers only half of thespinnerette to produce a temperature gradient.

In a particular embodiment, the cooling device 14 comprises a cylinder56 having mounted thereon top portions 58 and 60 and sides 62 and 64.The lowest portion of the cylinder 56 which is bevelled, forms with theside 62 and the top 58 a chamber 66 having a slot or gas outlet 68.Similarly the side 64 and top'60 forms a chamber 70 with gas outlet 72.Gas inlets l8 and 19are connected through cylinder 56 and feeds in thecooling gas in chambers 66 and 70, which then escapes 1m nni nInL'through 68 and 72. An amount of air in the order of about 1 s.c.f.m. persquare inch of slit has generally been found satisfactory to effectuateproper quenching in accordance with the invention. The top portion 58and 60 are better shown in FIG. 3 mounted on cylinder 56 with the gasinlets 18 and 19.

The gas jet may be any jet conventionally used. FIG. 4 shows a jet whichmay be used in accordance with the invention, where the ribbon 16 goesthrough inlet 72, moves along passage 74 and leaves the air jet throughoutlet 76 as a highly bright yam. In accordance with the invention theair could be fed perpendicular to the ribbon as at 78, or could also befed at an angle in the direction of the ribbon as shown by the dottedline at 80 or therebetween.

The final yarn is made of filaments having a rectangular cross sectionand having a luster index greater than 2 and generally greater than 4.Yarn of a total denier of 1,200-1,900, with a tenacity between 1.2-2.5g./d. and an elongation of between 8-15 percent is generally obtained.In the case of crinkled yarn, 10-12 crinkles per inch are generallyfound.

If a viscosity gradient has been set in polypropylene before extrusion,that is before leaving the die, the yarn may then be heat relaxed. Thisrelaxation is generally conducted in a hotair oven maintained between100 C. and 150 C., and preferably 125 C. The yarn may be moved in theoven by means of a set of driven rollers rotatably mounted in theinterior of the oven and on which the yarn is allowed to move for a fewseconds. During the relaxation operation, the yarn shrinks and producesa crinkled effect. There are numerous ways of setting viscositygradient. For example some means have been described in patentapplication Ser. No. 008,153, invented by Frank James.

Numerous variations of the basic process may be obtained as illustratedin the following examples.

- X M LE}.

Isotactic stabilized flakes having an intrinsic viscosity of 2.8 weremelt extracted in a Killoran, Barnett, Guay extruder, at a temperatureof 240 C., at a rate of l lb.lhr., through a slot 1.25 inches 0.030 inchon a die 0.020 inch thick. A gasket having a slot larger than the dieorifices prevented cooling of the die by an air flow that was blownthrough two thin slits on each side of the ribbon when it leaves theextrusion orifice. Being colled so rapidly, the ribbon had no time torelax and had a width of 1.1 inches. It was pulled at a speed of 50f.p.m. and immediately drawn at a ratio of 3 to 1 into a tube stretchermaintained at a temperature of 105 C. The drawn film was then passedthrough an entangling air jet at a speed of 200 f.p.m. A contraction ofabout percent was due to entanglement during this last operation. Ahairy lustrous yarn of isotactic polypropylene which comprises filamentsof rectangular cross section was obtained. A cross-sectional view of theyarn is shown in FIG. 5 under a magnitude of 200 times the original. Theyarn had a total denier of 1,600, a tenacity of 1.5 g./d., and percentelongation.

The luster index of the yarn obtained was compared against wool andnylon.

The yarn obtained from Example 1 was wound on a 2-by-2- inch aluminumplate in several layers until the background streaks or excessivehairiness. Using a Lumetron" type 402E Calorimeter adapted with agalvenometer, the pad which exhibited the highest visual luster wasinserted in the same holder with the yarns running parallel with theincident light beam. The photocell was set at an angle of 45 and theinstrument was balanced until the reflectance measure was near 90percent of the reading dial, which was recorded as the specularreflectance of the sample.

The photocell was then set at an angle of 90 and the reflectance wasmeasured as the direct-angle reflectance. The ratio of the specularreflectance at 45 reading over the directangle reflectance reading 90was obtained and is defined as the luster index. The luster index wasalso defined for the other two samples and are indicated in Table 1TABLE 1 LUSTER INDEX Specular Direct Angle Luster ReflectanceReflectance Index Wool 78.9% 48.4% 1.63

Nylon 90.0% 51.2% 1.76

Fibrillated PP 45.7% 10.8% 4.23

EXAMPLE 2 EXAMPLE 3 A hairy and bright yarn was obtained in processingpolypropylene stabilized flakes of a lower molecular weight (intrinsicviscosity 2.1) in the same extrusion machine as described in Example 1.Extrusion temperature was lowered to 220 C. and the material wasprocessed as in Example 1. The same type of material was obtained havinga total denier of 1,200.

EXAMPLE 4 The same polymer as used in Example 3 was'processed accordingto conditions described in Example 2, but drawn at a ratio of 2.7 to l.A self-crimped yarn was obtained in these conditions similar to the oneof Example 2.

Having thus disclosed the invention, what is claimed is:

1. A hairy, lustrous, self-crimping yarn of isotactic polypropylenewhich comprises filaments having rectangular cross sections, a lusterindex of 4, a tenacity between about 1.2 to 2.5 grams per denier, anelongation of between 8 to 15 percent, at least 10 to 12 crinkles perinch and a total denier of from 1,200 to 1,900.

